Hello Myleschalmers,
You can do GPT repartition of your eMMC drive by reflashing Android with a modified gpt.bin file. Click
Do not worry about that the link I added is for a different brand and model. This is what you need. You should download the ZIP file. Choose desired gptxxx.bin and rename it to gpt.bin. Then replace original gpt.bin in your rom folder and reflash Android with Intel Phone Flash Tool. You should choose flash.json.
After that you should reflash Windows.

Flashed android with the GPT, worked perfectly. I went for the 20. Perfect.

Reflashing Windows was a bit tricky but it is done. USB 3.0 on my Chuwi didnt recognise the flash card. So I switched it to the other USB port. Now I had the option to select it on F7. After flashing (I watched the script from start to end) - windows still wasn't on my machine. So I had to reflash again - this time - it was perfect and I now have both Windows and Android back, with Android on 20GB.

Windows is working perfectly, touch, wifi, bluetooth, display etc.

Thanks a lot for your work - I now have exactly what I wanted on the device at the right hard drive ratios. Much appreciated!

Your description may be clear to those with good technical knowledge, but, even though I am not technical I can normally do these sort of things. I did not know what the rom folder is, assuming it was on my tablet! I guess you mean the android zip file. When I add the gpt.bin file to the zip, it errors when I use the flash tool.

Your description may be clear to those with good technical knowledge, but, ev ...

Well, if things are so bad, then before flashing your tablet you should start with learning the basics of computer literacy. So this is the first lesson for you and I hope the last.
Follow all the steps on an external PC.
1. Download the ZIP file with the modified gpt.bin file from there.
2. Download the ZIP file with the Android ROM for your tablet from there.
3. Unblock these two downloaded ZIP files. Right click on a file => choose Properties => check Unblock box => click OK.
4. Extract (or UnZIP) these two downloaded ZIP files. Right click on a file => choose Extract All => select a destination => click Extract.
So, you got the extracted files and now you know exactly where they are, because you chose their destination in the previous step. You can do all the other steps to replace the original gpt.bin file with the desired one.
Replacing the gpt.bin file you have prepared your Android ROM for flashing.
So, flash Android with flash.json first as described in the tutorial, and then do Windows as described there.
Good Luck!